The present disclosure relates to a fuel property determining device and a combustion control device for an engine.
While a fuel property greatly influences combustibility (e.g., ignitability) of engines, the fuel property may significantly vary depending on the production area of the fuel, etc. Therefore, if the fuel property changes while a combustion control amount of the engine is constant, the combustibility greatly changes. JP2009-036027A discloses an art for retarding a fuel injection timing and detecting (determining) a cetane number as a fuel property based on the combustion state (misfire/ignition) when the retarded timing is applied.
If the retarding of the fuel injection timing for the fuel property determination is performed when the combustion state (combustibility) is good, since only a slight combustion variation occurs, it is difficult to accurately determine the fuel property. For example, in a case of retarding the fuel injection timing when the engine is idling so as to determine the fuel property, since the combustion state during idling changes depending on the environment, etc., the combustion variation is large at times and small at other times even with the same retarding amount of the fuel injection timing. This causes difficulty in determining the fuel property (degrade the determination accuracy). Note that although it may be considered to perform the determination only when the combustion state is within a given range, the frequency of the determination decreases in this case.